Electrofiltration system for purifying organic liquids

ABSTRACT

Non-petroleum organic liquids (fats, animal and vegetable oils, etc.) containing solids (e.g., hydrogenation catalysts) are purified within a unique electrofiltration system wherein the organic liquids are passed through a selected bed material in which is established an intense electric field for removing the solids. Upon solids-fillup of the bed, selective cleaning restores the bed for continued purification of the organic liquid stream. The purified organic liquid stream is monitored for indicating when the selective cleaning of the bed is required. The electrofiltration system, both in a novel electrofilter and process, produces without aging a new organic liquid product having comparable properties to multistep processed prior art organic liquid.

This is a continuation of application Ser. No. 721,140, filed Sept. 7,1976 now abandoned, which is a division of App. Ser. No. 636,261, filedNov. 28, 1975, now U.S. Pat. No. 4,040,926, issued on Aug. 9, 1977.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the removal of solids from an organic liquidby using electrical fields. The invention more particularly relates tothe removal from organic liquids of solids by their induced adherenceupon a particulate bed under the action of d.c. electrical fields.

2. Description of the Prior Art

Non-petroleum organic liquids include fats, vegetable and animal oilswhich may be used for human consumption, but are not necessarily limitedto such utilization. These organic liquids can be purified by removingsolids to improve chemical properties, color and visual appearance, andfor other reasons. In one example, the hydrogenation of edible oils forpreparing more suitable products for human consumption has been knownfor nearly one hundred years. The modern hydrogenation process foredible oils originated in research work conducted at the turn of thiscentury. In this process, the edible oils, such as cottonseed, soybean,and corn oil, are placed within a reaction vessel (commonly termed a"converter") and brought into contact with hydrogen at elevatedtemperature and pressure in the presence of a small amount of metalhydrogenation catalyst. For example, the catalyst is usually present insmall amounts which may range from 0.01% to about 0.5% by weight basedupon the total weight of the edible oils subjected to hydrogenation.Various types of hydrogenation catalysts, such as copper chromite, areknown for providing the reaction between hydrogen and the edible oil.For example, one commercial hydrogenation catalyst includes the metalnickel as the principal catalytic agent, but it also may have minoramounts of copper, alumina, or other materials. The metal hydrogenationcatalysts are employed principally in a finely defined divided form andare prepared by special methods. Commonly, the nickel metal is placedupon a finely divided, highly porous, inert refractory material, such asdiatomaceous earth, or other highly siliceous material. The catalyst issuspended in the edible oils during the hydrogenation process asoil-coated inert solids, which may adsorb soaps or other impuritiesfound in the oil. After the hydrogenation reaction is completed to thedesired degree, the hydrogenation reaction materials are removed fromthe converter. Then, these materials are passed through a filtrationsystem for removing the inorganic solids from the hydrogenated edibleoil product.

Various inorganic materials are added to the hydrogenated edible oilproduct to enhance its filterability. Filteraids usually are employed topromote the product filtration procedure. Various types of relativelysophisticated and expensive filtration equipment are employed.Generally, pressurized filter press assemblies are used, in parallelflow arrangements, to pass the product through a multitude of filterelements which may comprise screen supports carrying paper, canvas orother types of filter medium. These filter elements may be precoatedwith some type of diatomaceous earth or filteraid to improve oilfilterability. The hydrogenated edible oil product is passed throughthese filters to remove as much as possible of the hydrogenationcatalyst material and other inorganic solids materials. However, thefilters cannot remove substantially all of the inorganic solids.Additionally, the filters pass decreasing amounts of inorganic solids asthe filtration procedure progresses towards an ultimate removal level.

The edible oil industry employs two basic tests to determine theeffectiveness of filtration on a hydrogenated edible oil product. In onetest, a pound of the edible oil is passed through a filter disc atregulated physical conditions of temperature and time. The filter discretains impurities above a certain size magnitude leaving a "dark spot"which is compared to a standard set of filter discs. The test is knownas the "Filter Disc Impurities Test." The standard discs are numbered 1through 10, with number 10 being that disc which shows no change in"color" over the unused filter disc. Another test is the analysis of theedible oil for nickel content. The filtration procedure produces anedible oil with from one to several parts per million (ppm) of nickelcontent. For consumer acceptance and long term storage and otherreasons, the nickel content is preferred to be less than 1 ppm ofnickel.

Mechanical filtration equipment employed in the edible oil industryusually passes some solids during the filtration procedure. As anexample, the edible oil product has a color of relatively low value,e.g., 4, at the beginning of filtration, but then its color test rapidlyimproves towards a filter disc color of 9 or better. For this reason,the filter equipment cannot produce throughout the edible oil filteredproduct a filter disc color of 9 or better.

The filtered edible oil, at elevated temperatures, is subjected toadditional treating steps which may include treatment with bleachingearth, phosphoric or citric acid or other metal scavengers, with theaddition of filteraids, so that the finely divided residual inorganiccatalytic and other solids are removed. The edible oil accepted byconsumers must have a color of 9 or better. Thus, filtration or othercolor improvement procedures are employed with each edible oil subjectedto the hydrogenation. Substantial time elapses in these procedures andsubjects the edible oils to aging. The procedures are practiced untilthe edible oil has a filter disc color of 9 or better, and residualhydrogenation catalyst solids, and possible colloidal nickel metal, isat an acceptable low value.

Nearly forty years ago, it was proposed to purify edible oils by addinga small amount of a loader-type solids, such as "10% activated clay" ina finely divided admixture to the edible oil. This mixture was thenflowed horizontally in a zigzag path between closely spaced electrodeswhich were energized to elevated potentials. The impurities and theloader solids were to migrate to one or the other electrodes for theirremoval from the edible oil. Accumulated solids might "drop off" afterreaching a certain thickness on the electrodes or they could be removedby interrupting or reversing the current. Mechanical removal of thesolids from the electrodes could also be used. Unfortunately, theunpacked dielectric zone between the electrodes will not removesubstantially all of the impurities from the edible oil. One reason forthis result may be that the electric field cannot be made of sufficientintensity even with closely spaced electrodes that substantially all ofthe inorganic solids could be removed from the edible oils. Some solidspass through the spaces between the electrodes without being attractedto them for removal from the edible oil.

It has been proposed for nearly as many years to employelectrofiltration systems for removing inorganic and organic solids fromdielectric natural and petroleum oils. For this purpose, the dielectricoil carrying the solids is passed through a particulate material withinan elevated d.c. electric potential field. The d.c. field can havepotentials of between 5 and 200 kilovolts established across the bed.The bed might be composed of particles of materials such as furnaceslag, sand, gravel, limestone, crushed glass, glass bead, ceramics,palletized clay, and like solid materials. Various types of electrodearrangements have been advocated for providing the high voltage d.c.electrical field for these electrofilter devices. The electrofilterdevices, which have been known in the past, have been highly effectivefor removing inorganic solids from dielectric liquids such as thehydrocarbon products of crude oil refining. Unfortunately, theseelectrofilters are very effective in attracting solids to theparticulate bed materials. These removed solids adhere very strongly tothe bed material even with the d.c. electric field removed from theelectrofilter device. Once the bed is subject to a solids-fillup,substantial changes in electrical conductivity occur which induce arcingin many instances. Arcing can produce a sudden release of solids intothe dielectric liquid- Then, the bed must be cleaned before beingreused.

The tenacious adherence of inorganic solids upon the particulate bed ofelectrofilters has required special techniques for regeneration. Examplemay be taken to U.S. Pat. Nos. 3,394,067, 3,799,855, 3,799,856 and3,799,857 for illustrations of various types of practical and commercialbed cleanup systems. These patents describe cleanup procedures whichproduce a very high mechanical agitation between the particles of theelectrofilter bed for mechanically removing adhering inorganic solids.Naturally, high levels of mechanical contact between these particlescause abrasion and could result in a small amount of abraded particlematerial being released from the bed. As a result, the bed would have tobe scrupulously cleaned of the small fragmented portions of theparticulate material unless these residues were not critical to thedielectric liquid being treated. In the electrofiltration purificationof hydrocarbon materials, such as distillates and residual streams orinorganic materials, a small amount of residue from abraded particulatebed material would not be a problem. However, these abraded materialsare intolerable in edible oils.

The prior art has included proposals to employ electrofiltration forpurification of various types of dielectric organic liquids for aboutfour decades. However, no electrofilter device has produced thepurification of organic liquids which contain finely-divided inorganicand organic solids for several important reasons. In the first instance,the electrofilter equipment must effect complete removal from solidswithout either an unacceptable pressure buildup or deleterious change inelectrical characteristics inducing arcing, shorting and like problems.In the second instance, the electrofilter must be capable of handlingeffectively the organic liquid stream containing widely varying amountsof solids. In the third instance, the electrofilter system must containa particulate bed material of special characteristics so that (1) theorganic liquid product is produced with extremely low amount of residualsolids, without undue pressure buildup or arcing, (2) the particulatebed material is readily cleaned of adhering solids, and (3) no abrasionor loss of the particulate bed material itself occurs to contaminate theorganic liquid. The foregoing reasons summarize the incapability ofprior art electrofiltration system in being used in the purification oforganic liquids containing finely divided solids.

The present invention is an electrofiltration system for purifyingorganic liquids by removal of finely-divided solids without theforegoing recited problems of prior art electrofilters. In particular,the present invention is a novel electrofilter, electrofiltrationprocess, and organic liquid product. A selected material in the bed ofthe electrofilter system produces a substantially complete removal ofthe solids, irrespective of the solids loading content, and without theelectrofilter system having any appreciable pressure buildup orelectrical arcing in the bed. The bed is chemically inert, and nocontamination of the organic liquid stream occurs in use. The cleaningof the bed of accumulated solids is not complicated and produces anenvironment for continuous and repeated electrofiltration for producinga product organic liquid equal in physical and chemical characteristicsto commercial product prepared by extended time, multistep procedures.Additional features of the present invention will be appreciated fromthe following description.

SUMMARY OF THE INVENTION

In accordance with this invention, there is provided anelectrofiltration system, including apparatus, process, and product, forthe purification of an organic liquid stream of high resistivity. Inparticular, the organic liquid stream, at suitable temperature, ispassed through a chemically inert bed having mutitudinous flow channelsbetween rigid masses of a solid material having a dielectric constantnot in excess of about 7. A d.c. electric field within the bed providesa sufficient intensity for removing solids from the organic liquidstream by the electrically induced adhesion of the solids on thematerial to provide a purified organic liquid stream removed to asubsequent utilization. The bed material, at least in part, isselectively cleaned of adhering solids by interruption of the electricalfield, passing a cleaning fluid through the material to remove adheringsolids, and then removing the fluid with the removed solids from thematerial being cleaned. In a preferred embodiment, the purified organicliquid stream is monitored to provide an indicating signal when toundertake the selective cleaning of the bed material. The purifiedorganic liquid stream is a novel product, quickly prepared withoutaging, and having comparable chemical and physical properties toconventional multistep treated commercial product.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatical illustration, in flow schematic, of thepresent electrofilter system applied to a prior art hydrogenation plantfor producing edible oil as an example of an organic liquid;

FIG. 2 is a vertical cross-section illustrating the construction of theelectrofilter shown in the system of FIG. 1; and

FIG. 3 is a graphic comparison of several bed materials employed in theelectrofilter of FIG. 1 and a typical mechanical filtration relative tothe filter disc impurities color of an edible oil purified in thepresent electrofiltration system.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The present electrofilter system will be described in the purificiationof one type of organic liquid, namely, an edible oil. However, it willbe appreciated that the invention is equally applicable and of utilitywith other types of organic liquids, e.g., fats, animal and vegetableoils. Referring now to FIG. 1, there is shown an embodiment of thepresent electrofilter system associated with an appropriate portion of aprior art hydrogenation plant, wherein edible oils are contacted withhydrogen at elevated temperature and pressure in the presence of afinely-divided catalytic material. More particularly, the hydrogenationplant 11 is enclosed within the chainline 12 with the designation ofprior art being applied as an example of commercial operations. Anedible oil, such as soybean oil, is brought from storage through aninlet conduit 13 and a heat exchanger 14 directly into the hydrogenationconverter 16. The heat exchanger 14 raises the temperature of the edibleoil to a suitable level, e.g., above 250° F. The converter 16 is a steelvessel usually with an upright axis which contains the charge of edibleoil to be hydrogenated. The edible oil in the converter is admixed witha suitable amount of metal catalyst. In most instances, a diatomaceousearth or a filteraid material is intermixed with the catalyst insuitable proportions with an edible oil carrier in the catalyst mix tank17. Then, this mixture is displaced by pump 18 through a control valve19 into the converter 16. The converter 16 usually has an internal mixerarrangement for maintaining a suspension of the catalyst materialswithin the edible oil. Hydrogen is added to the converter 16. Thehydrogenation reaction takes place over a suitable length of time, suchas one hour, depending upon the mass of edible oil charge and thedesired hydrogenation degree to be produced in the edible oil product.

The converter 16 may be of any suitable size. For description, theconverter 16 will receive an edible oil charge of about 40,000 pounds,and the hydrogenation catalyst material is of the nickel metal variety,which is introduced to a suitable concentration of between 0.01 and 0.05percent by weight. The nickel catalyst is approximately 25% by weight ofnickel with the remainder being Kieselguhr or other diatomaceous earthmaterial.

After the hydrogenation reaction is completed, the contents of theconverter 16 are moved through the valve 21 into a drop tank 22 wherethe hydrogenated edible oil product is held while being processed forthe removal of the finely-divided hydrogenation catalyst and otherinorganic solids. Presently, the contents of the drop tank 22 are movedthrough a control valve 23 by centrifugal pump 24, an optional heatexchanger 26, and through a piping loop containing several controlvalves to the inlet 27 of the filter press 28. The filter press isconventional with a plurality of filter elements. The filtered edibleoil is removed from the filter press 28 through the outlets 29 or 31depending upon whether the sections are operated in parallel or inseparate sections. The outlets 29 and 31 connect to a filtered edibleoil line 32 for directing this stream to subsequent processing for theremoval of residual amounts of the hydrogenation catalyst and otherinorganic solids.

For example, the filtered edible oil in the line 32 may contain aboutseveral parts per million of nickel metal (suspended and colloidal) soas to have a pronounced green-to-black color, and several parts permillion of inorganic solids, such as filteraid, and a filter disc colorof 6 or worse. Thus, the filter press 28 cannot produce an acceptableedible oil product that could be used for human consumption. Thefiltered edible oil in line 32 now usually is subjected to additionalprocessing steps. One step is treatment with citric acid or phosphoricacid and a filteraid material, and filtration to remove the chelatedhydrogenation catalyst. Another step is a bleaching operation wherein asmall amount of bleaching clay is added to the edible oil, and thenfiltered to provide the edible oil product. The edible oil product afterone or more of these steps is an edible oil product directly suitablefor consumer use. Sometimes, this product is subjected also to awinterizing and/or deodorizing step to produce certain types of edibleoils.

In the present invention, all mechanical filtration steps are avoided.The hydrogenated edible oil in the drop tank 22 is passed through thenovel electrofilter system of the present invention. Referringspecifically to that portion of FIG. 1 outside the chainline 12, theedible oil from the drop tank 22 is diverted through the block valve 33into a raw oil line 34. The edible oil in the line 34, by use of theheat exchanger 26, is adjusted in temperature, usually above 150° F., sothat organic solids, such as stearine, are in total solution in theedible oil stream and cannot plug the electrofilter. The line 34connects into an inlet manifold 36 associated with the electrofilter 37.The manifold 36 has a plurality of motor control valves 35, 38, and 39,whose functions will be hereinafter described. With this arrangement ofthe inlet manifold 36, the edible oil is passed upwardly through theelectrofilter 37 and removed through the outlet manifold 42 whichincludes motor control valves 43 and 44. However, it may be desired tohave the edible oil passed downwardly through the electrofilter 37 andthe functions of the inlet and outlet manifolds would then be reversed.The piping for the present system is arranged for this purpose as willbe appreciated by examination of the respective manifolds and theirconnections into the system shown in FIG. 1.

The electrofilter 37 is arranged so that substantially all of theundissolved solids, including the hydrogenation catalyst, filteraid,diatomaceous earth, etc., and any insoluble organic solids, are removedfrom the edible oil stream. The electrofilter 37 has a selected bedforming an inner electrode space subjected to a high intensity d.c.electric field for removing substantially all of these solids from theedible oil. The purified edible oil stream is removed through a productline 46 and a three-way control valve 47 into an edible oil productconduit 48 for removal to a subsequent utilization. Preferably, theedible oil product line 46 includes a monitor of the purified edible oilproduct from the electrofilter 37 to determine the approach of asuddenly increased solids content which occurs on the apporach ofsolids-fillup in the bed of the electrofilter 37.

The present invention involves the selection of a certain type ofmaterial forming the bed of the electrofilter 37. The bed is chemicallyinert and has multitudinous flow channels between rigid masses of asolid material. The bed material should have a dielectric constant notin excess of about 7. The bed material should have sufficient rigidityso that in operation it cannot be compressed in a degree to reduce theflow channels, thereby producing an unacceptable pressure drop acrossthe bed.

One of the characteristics of the electrofilter 37 with this selectedbed is that substantially all of the solids, including even colloidalnickel and filteraid materials, are removed from all the edible oilpassing into the product line 46, and this purity is maintained untilthe bed has accumulated its capacity of removed solids as thesolids-fillup condition is approached. As this solids-fillup conditionis approached in the bed of the electrofilter 37, no significant changesoccur in the electrical parameters or measurable physical operationconditions concerning the electrofilter. However, there is a suddenincrease in the solids content of the treated edible oil. Moreparticularly, the pressure drop across the electrofilter 37 is small anddoes not change within the measurement error of conventional pressureguages. In addition, no significant change in electrical parameters,voltage or current, occurs in the high voltage electric field imposedupon the bed within the electrofilter 37. These phenomena of theelectrofilter 37 are more apparent from the following discussion of thepreferred design and operation of the electrofilter 37.

The edible oil treated in the electrofilter 37 enters the product line46 in such a completely purified form, relatively free of inorganicsolids, colloidal metals, etc., that it has a unique appearanceclassified by experienced workers in the food industry as "bright andclear" in appearance. Edible oil of this bright and clear appearance hasa filter disc impurity number generally of about 10. The reason for thisunexpected product result is not completely understood except that theelectrofilter 37 produces substantially complete removal of nickelcatalyst, colloidal nickel, and other solids from the edible oil. Inaddition, the electrofilter 37 maintains the production of outstandingedible oil product until the solids-fillup condition of the bed of theelectrofilter 37 is reached. Only at this solids-fillup condition doesthe edible oil entering the outlet manifold 42 rapidly deterioratetowards the properties of the raw edible oil flow in the line 34 fromthe drop tank 22.

As a result, the electrofilter 37 for maximum efficiency and bestoperation requires a mechanism to predict the onset of this rapiddeterioration in edible oil quality when solids-fillup of theelectrofilter bed is reached. One means of accomplishing this result isby a fixed time cleaning cycle. Alternatively, the initial appearance ofa small amount of inorganic solids in the edible oil within the productline 46 can be detected as solids-fillup condition is approached. Whenthe electrofilter 37 is operating satisfactorily, the edible oil inproduct line 46 is bright and clear in appearance and also shows noTyndall effect. At the very onset of solids-fillup in the bed of theelectrofilter 37, a slight Tyndall effect occurs in the edible oil. Ifdesired, a sight glass 49 is placed in the product line 46 to detectthis Tyndall effect. A narrow beam, high intensity light, through thesight glass 49 displays the occurrence of the Tyndall effect. At thistime, the electrofilter 37 is "shut down" for a selective cleaning ofthe bed by the thorough removal of adhering inorganic solids.

If desired, the monitoring of the edible oil stream for the occurrenceof increased solids content can be undertaken by a monitor 51, includingan optical cell 52 in the product line 46, to provide an output signal53. The monitor 51 may be a nephelometer. The output signal can give avisual or arcual indication to an operator. Preferably, the outputsignal is adapted to adjust the various valves and other switchingfunctions for cleaning the electrofilter 37. The controller 54 uponreceipt of the output signal can provide a plurality of output signals56 to operate the various control valves associated with theelectrofilter 37, conduct the stepwise sequence of cleaning steps in theelectrofilter 37, and control the operation of a high voltage powersupply 40 which is associated with the electrofilter 37. The controller54 may be convenient and employ either pneumatic or electrical controlsignals 56 in the necessary sequencing functions for the desired controlof the various elements associated with the electrofilter 37. The d.c.electrical field in the electrofilter 37 is removed from the bedmaterial for the cleaning process.

The bed material in the electrofilter 37 is cleaned at least in part,but preferably in its entirety by use of a cleaning fluid. Also, the bedmaterial may be cleaned in place, externally or in any manner whereinthe cleaning fluid flow removes solids from the material. If desired,the cleaning fluid may be a portion of the raw edible oil in line 34taken from the drop tank 22. In other instances, it may be desired touse other liquids for cleaning the bed material of the electrofilter,such as edible oil product taken from the conduit 48. The cleaning fluidcan be used in a single pass mode but preferably is recirculated in thecleaning process. In one example, edible oil as a cleaning fluid isplaced into the charge tank 57 wherein its temperature can be elevatedas desired by use of a steam heating system 58. Then, the pump 59 movesthe edible oil through the cleaning line 61, and with the block valve 62in a closed position, the edible oil flows into the inlet manifold 36 topass upwardly through the electrofilter 37 into the outlet manifold 42.The circulating edible oil returns in the line 46 through the three-wayvalve 47, the return conduit 63 through block valve 64 and then into thecharge tank 57. However, the electrofilter may be also cleaned withdownflowing edible oil. The circulating flow through the cleaning line61 of edible oil is adjusted in rate so that the bed of theelectrofilter 37 is only slightly expanded but not displaced ormechanically abraded in the absence of the d.c. electric field. Theedible oil in the charge tank 57 containing the removed solids can bepassed through the filter press 28 for recovery of the edible oil whichmay then be recycled through line 34 and the electrofilter 37.Alternatively, this mixture of edible oil and solids including catalystmay be recycled into the converter 16 for reuse.

Preferably, the cleaning process is carried out in the electrofilter 37by first terminating the flow through the line 34 of the edible oil fromthe drop tank 22. Then, the valved manifolds are arranged so that a flowof nitrogen from the line 66 is passed downwardly through theelectrofilter 37 to displace the residual liquid volume of purifiededible oil into the product line 46 and through the valve 47 into theedible oil conduit 48. In this manner, the amount of "slippage" orrecycle of purified edible oil is minimized in the use of theelectrofilter 37. As long as the power supply 40 is energized and anelectric field exists in the bed material of the electrofilter 37, theadhering solids will not be displaced from the bed by the flow ofnitrogen. Then, the flow of nitrogen through line 66 is terminated andthe power supply 40 is de-energized. The cleaning fluid can now becirculated through the electrofilter 37 as previously described.

The volume of the circulating cleaning fluid is not as critical as theflow rate through the bed of the electrofilter 37 which will usually bein the range of at least 16 inches per minute superficial velocitythrough the bed material. Under those conditions, the volume ofrecirculating cleaning fluid may be as small as three times the liquidvolumetric capacity of the electrofilter 37. The optical properties ofthe cleaning fluid and entrained solids flowing through the line 46 canbe employed to determine when ultimate cleaning of the bed material hasoccurred since solids amounts become constant. For example, the monitor51 reaches a peak reading of opacity which indicates the end of thecleaning cycle. At this time, the cleaning fluid is removed from theelectrofilter 37 by switching the necessary valves to be displaced bythe incoming edible oil in line 34. Preferably, the cleaning fluid isdisplaced from the electrofilter 37 by a small quantity of the edibleoil product from the product line 46. Alternatively, nitrogen is appliedthrough line 66 (as previously described) to displace the liquidcontents of the electrofilter 37 downwardly through the manifold 36 andinto the various lines and conduits for its recovery. Now, the bedmaterial of the electrofilter 37 is clean and can be returned topurification of the raw edible oil in line 34. The power supply 40 isenergized, the valves adjusted to reinstate the operation ofelectrofilter 37, and the flow of the edible oil through the conduit 34from the drop tank 22 is resumed. Thus, the electrofilter 37 employs aselected bed material which not only produces optimum cleaning of theedible oil, but also permits ready cleaning of adhering solids.

The electrofilter 37 has a suitable construction which in one embodimentis illustrated in vertical section in FIG. 2. The electrofilter 37comprises an upright vessel 71 having inlet connections 72 connected tothe inlet manifold 36 and an outlet distributor 73 connected to theoutlet manifold 42. Preferably, the inlet 72 is provided by a pluralityof well screens 74 which are dimensioned so as to prevent the passage ofthe material 76 comprising the bed 77. Energized electrodes arepositioned within the bed 77 and may take any usual form. For example,an inlet bushing 78 extends upwardly into the vessel 71 and carries aspider 79 on which are mounted in a concentric arrangement an energizedrod 81, and metal cylinders 82, 83 and 84. The rod 81 is connected by alead 86 to the power supply 40 so that the electrodes carried on spider79 are energized to a d.c. potential relative to the grounded shell ofthe vessel 71. A similar system of grounded concentric electrodes issuspended from a spider 87 supported upon a mounting bracket 88 carriedabout the internal perimeter of the vessel 71. Suspended from the spider87 in concentric relationship are a plurality of cylindrical electrodes89, 91, and 92. It will be apparent that the concentric relationship ofthe energized and grounded cylindrical electrodes provide forestablishing an electrical field within the bed 77. For example, thespacing between the energized and grounded electrodes can be one inchwith a like spacing about the rod electrode 81 and to the internalcylindrical surface of the metal shell of the vessel 71. With thisarrangement, the power supply 40 should provide at least 20 kilovoltsper inch d.c. electrical potential to lead 86. Preferably, the powersupply 40 provides a d.c. potential of at least 40 kilovolts per inchwithin the bed 77. Excessive high intensity potentials in the d.c.electric field within the bed 77 should be avoided. Excessively highd.c. potentials could lead to gas (hydrogen) ionization and arcingwithin the electrofilter 37. The finely-divided solids carried in theedible oil into the bed 77 are acted upon by the d.c. electric fieldwhich electrically induces the adhesion of these solids onto thesurfaces of particles 76. For practical purposes, no solids can escapethe bed 77 in the presence of the d.c. electric field until thesolids-fillup condition is reached. The electrically induced adhesion ofsolids is so great a force that a flow of nitrogen gas equal in rate tocleaning fluid flows cannot remove them. However, removal of the d.c.electric field allows a simple washing of the bed to remove completelythese solids. The electrofilter 37 is a system similar to knownelectrofilters having particulate materials in their inner electrodespaces. However, the particular selection of the particles 76 formingthe bed 77 of the present electrofilter 37 produces an electrofiltersystem unique in apparatus and process, and this system producesunexpected purification of organic liquids, such as oil streams, into abright and clear product equal to commercial products obtained bymultistep filtration procedures.

More particularly, the bed 77 of the electrofilter 37 is preferablycomprised of chemically inert, hard granular particles of a rigid, andsubstantially incompressible material. Furthermore, these particles arein the majority non-spheroidal with a relatively discontinuous surfaceconfiguration and a dielectric constant not in excess of about 7 (at 1kilohertz). The term "non-spheroidal" is intended to include bydefinition particles other than true spheres, such as oval and othernon-round shapes having minor to major axes in ratios exceeding 4 to 6.By the terminology "relatively discontinuous surface configuration" ismeant a surface that is not planar or unbroken such as the surface of aglass bead, and particularly included are multifaceted particles havingmeeting edges between multitudes of small surfaces which may be planar,concave, convex and combinations thereof, regular or irregular inarrangement.

The exact reason for the novel functioning of the bed 77 in theelectrofilter 37 cannot be determined with an exact scientificdefinition. However, it is believed that the particularly selectedparticles 76 in conjunction with the electrical characteristics of theorganic liquids (e.g., edible oil) and the contaminating solids, such asthe metal hydrogenation catalyst and filteraid, interrelate to producethe novel results of the present invention. For example, edible oilshave a dielectric constant of about 3.5. The diatomaceous earth carrier(Kieselguhr), the metal hydrogenation catalyst, and filteraid all have adielectric constant of about 4. The metal hydrogenation catalyst and thefilteraid materials have highly developed pore surfaces which appear tobe completely saturated with edible oil. The particles 76 which areselected for the purpose of the present invention also have a dielectricconstant not greatly in excess of about 7, and preferably below about 5.Thus, all of the dielectric materials within the electrofilter 37 havevery similar dielectric constants, and all these materials haveextremely high resistivity (e.g., 1×10¹⁵ ohm-cm) and dielectric strength(e.g., above 10 kv, dc/mm). It is believed that these dielectricproperties permit the bed 77 to function exceptionally within the highintensity d.c. electric field for electrically inducing the tenaciousadhesion of the solids, such as filteraid, to the particles 76. However,terminating the d.c. electric field within the bed 77 allows theadhering solids to be easily removed by a relatively low rate of flow ofa cleaning fluid without disruption of the particles 76. For example,the electrofilter 37 will operate to remove solids with a flow of 12inches per minute superficial velocity of edible oil through the bed 77.However, the particles 76 in the bed 77 are cleaned thoroughly (with thed.c. electric field removed) at the flow rate of above about 16 inchesper minute superficial velocity with edible oil as the cleaning fluid.The bed 77 does not need to be made turbulent or suffer particlemovement, but preferably, it merely expands slightly during the flow ofcleaning fluid.

The particles 76 should be chemically inert and not contaminate theedible oil. The particles 76 should have a relatively discontinuoussurface configuration in contrast to a highly polished smooth surfacesuch as glass bead or marble. In addition, the particles 76 should havea relatively high density or specific gravity and a substantial hardnesscompared to the solids which are to be removed. Particles selected foruse in the present electrofiltration system are preferably mineralscontaining crystalline silicon dioxide such as flint, garnet, graniteand fused quartz. These particles 76 selected from this mineral grouphave a hardness value of at least 7 on the Mohs scale of hardness, aspecific gravity between about 2.5 and about 2.9, a dielectric constantof about 4, and a discontinuous surface configuration provided innature. The particles 76 may range in size from about 1 mm to about 13mm for good results. A crushed flint with an average (50 percentile)particle size (smallest dimension) of 2.5 mm gives excellent results.These particles in the electrofilter 37 will not contaminate the edibleoil during either electrofiltration or the cleaning cycle for removingadhering solids from the bed 77. In addition, these particles provide anunexpected ease in cleaning the adhering solids from the bed 77 with acleaning fluid.

An experimental electrofilter system was placed into a commercial edibleoil refinery and tested with several edible oils and bed materials todocument the outstanding results. The experimental system wasessentially similar to that illustrated in FIG. 1 using theelectrofilter 37 shown in FIG. 2. The electrofilter was a cylindricalmetal vessel having a 15 inch internal diameter with a 30 inch totalvertical height. The vessel was placed on an upright axis and arrangedwith electrodes as is shown in FIG. 2. The concentric electrodes had anengagement length (taken in the vertical) of 14 inches. The interior ofthe vessel was substantially filled with selected particles according tothe guidelines of the present invention. A one inch spacing of theelectrodes existed over their engagement length. The electrodeselectrically confined in the bed 1.4 cubic feet of these particles. Thepower supply energized selectively these electrodes to between 20 and 40kilovolts. An edible oil stream of soybean oil was taken directly fromthe drop tank of the commercial operation. The drop tank held thehydrogenation edible oil which contained nickel metal in the amount ofseveral hundred parts per million and solids of several hundred partsper million. The experimental electrofilter system was operated on thisedible oil charge under precise test procedures on three types ofparticle media, designated as F-11, M-1, and G-1. These media werecommercial Flintabrise® brand sandblasting materials which arecommercially available from Clemtex Limited of Canada at Houston, Texas.More particularly, the media F-11 was a crushed flint rock with anaverage (50 percentile) particle size (least dimension) of 2.5millimeters. The media M-1 was a commercial "No 1 marine sand" which hadbeen screened so that all particle sizes were between 8 and 20 mesh onTyler standard screens. The media G-1 was a river gravel (granite) whichhad been screened to sizes between one-fourth and one-half inch. Thesemedia are all minerals containing crystalline silicon dioxide, havespecific gravities between about 2.5 and about 2.9, dielectric constantsless than about 5 and usually about 4, and high dielectric strengths.All media were scrupulously cleaned by carefully screening,water-washing, and air-drying so that no possible contamination of theedible oil stream could occur. Each media was placed within theexperimental electrofilter and subjected to test conditions of the samenature as described for the electrofilter 37. The incoming raw edibleoil stream was taken directly from the drop tank 22 and passed upwardlythrough the electrofilter at a rate of about 9 gallons per minute and attemperatures between 150° and 200° F. The product edible oil stream fromthe electrofilter was tested in accordance with the filter discimpurities test, analyszed for nickel content, and visual appearance.The total throughput volume of the electrofilter was recorded until theonset of product edible oil degradation by increased solids contentarising from the onset of solids-fillup of the bed of the electrofilteras detected by the initial observance of a Tyndall effect. The data fromthese tests of the media are set forth in the following Tables 1, 2 and3.

                  TABLE 1                                                         ______________________________________                                                       Filter           Vol/  Appear-                                 Media F-11     Disc    Ni/ppm   gal   ance                                    ______________________________________                                        40 kv @ 0.13-0.30 amps                                                                       8+      --        178  Clear                                   Rate 7.5-9 gpm edible oil                                                                    10      1.0       326  Very                                    @ 165° F.                      Clear                                                  10       .7       823  Clear                                   Bed loading 6.4 lbs./ft..sup.3                                                               10      --       1010  Clear                                                  10      --       1295  Clear                                                  10      3.4      1416  Clear                                                   9      --       1656  Clear                                                   4      --       1895  Gray                                                                          Tint                                    ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                                      Filter           Vol/                                           Media M-1     Disc    Ni/ppm   gal  Appearance                                ______________________________________                                        40 kv @ 0.2-0.22 amps                                                                        8      --        98  Clear                                     Rate 6-7 gpm edible oil                                                                      7      --       168  Clear                                     @ 185- 192° F.                                                                       10      --       --   Very Clear                                Bed loading 3.8 lbs./ft..sup.3                                                              10      --       359  Very Clear                                              --      --       408  Very Clear                                              10      --       --   Very Clear                                              10      --       654  Very Clear                                              --      --       925  Dark Gray                                 ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                                      Filter                  Appear-                                 Media G-1     Disc    Ni/ppm   Vol/gal                                                                              ance                                    ______________________________________                                        30 kv @ 6.0-3.0 amps.                                                                       10      0.2       170   Clear*                                  Rate 8-9 gpm Edible oil                                                                     10      1.1       441   Clear                                   @ 202- 194° F.                                                                       9+      --        580   Clear                                   Bed Loading 7.3 lbs./ft..sup.3                                                               9      --        855   Clear                                                  9      --        993   Clear                                                 --      --       1131   Clear                                                 --      --       1166   Clear                                                 8+      --       1276   Clear                                                 8+      0.9      1399   Clear                                                  6      --       1523   Hazy                                    ______________________________________                                         *Slight Tyndall effect                                                   

Inspection of the three Tables illustrates the unique operation of theelectrofilter system of the present invention in producing a productedible oil which consistently contains no inorganic solids and also hasa nickel content of about one part per million. Additionally, the edibleoil product was characterized by employees of the food industry as"bright and clear." No Tyndall effect was observed in "clear" appearancein the edible oil product. Unexpectedly, the product edible oil had a"clear" appearance until the filter disc color went from 10 to 8 whenthe Tyndall effect indicated the approach of a solids-fillup conditionin the bed of the electrofilter. Some slight Tyndall effect wasindicated initially with the media G-1, but this was believed to haveoccurred as a result of the start-up operation on the excessively largesizes of the media employed in the bed of the electrofilter.

The data from the above Tables is represented graphically in FIG. 3,wherein the throughput capacity of the experimental electrofilter isdisplayed as one axis while the other axis displays the filter discimpurities number of the edible oil product. It is noted that the mediaF-11 gave outstanding results, and it is preferred for the purposes ofthe present invention. The other media, G-1 and M-1, also gaveacceptable results. However, the media M-1 did not have the capacity toremove inorganic solids as do media F-11 or G-1. All three media doindicate that the edible oil product maintains outstanding purity untilthe onset of solids-fillup of the bed in the electrofilter. Then, thedeterioration by increased inorganic solids content in the edible oil isvery sudden and pronounced. The curve denoted "A" is one example of thefiltered edible oil produced by a commercial filter press operation inan edible oil plant wherein the filter disc impurity varies from about 2to about 6. The initial nonlinear portion of the media F-11 and M-1curves (until about 400 gallons throughput was reached) is believed toreside in bringing a relatively small volume pilot plant unit ontoequilibrium conditions at 9 gallons per minute connected to a drop tankhaving several ten thousands pounds of hydrogenated edible oil. Slightfluctuations in temperature and pressure occurred during the startupwhich may also explain these abnormalities.

An acceptable edible oil product in the commercial operations, afterbleaching or acid treating, and several filtrations, has a filter discimpurity color of 9. In comparison, the electrofilter of the presentinvention produces the maximum quality of edible oil product in onequick step which may take less than two minutes in commercialoperations.

The edible oil product from the electrofilter system of the presentinvention at any time before the onset of solids-fillup of the bed has afilter disc color of 10 on an average basis, a nickel content of about 1ppm, and a visual appearance of bright and clear. This edible oilproduct from the electrofilter, without any subsequent treatment, isequal in chemical and physical properties to the commercial productobtained by several filtration steps taking several hours within thepresent day commercial food industry plant. In addition the edible oilproduct from electrofiltration is substantially free from all suspendedand colloidal inorganic and organic solids. For example, the nickelcontent of the edible oil taken from the drop tank 22 is in the range ofseveral hundred parts per million. It is believed that the colloidalnickel content of this oil is substantially in the tens of parts permillion. However, the edible oil product provided by the experimentalelectrofilter always averaged in the range of about one part per millionor less of nickel content. Thus, edible oil product produced by thesystem of this invention is equal in appearance, and physical andchemical properties to that edible oil product of the commercial plant.

Returning to FIG. 1, the electrofilter 37 upon initial installationshould be scrupulosly cleaned so that the particulate bed does notcontain any type of deleterious material which can enter the edible oil.For this purpose, the electrofilter 37 can be flushed with a heatedvolume of commercial edible oil from the charge tank 57, cleaning line61 and through the valved manifolds. In addition, steam can be appliedthrough the line 66 to displace congealed edible oil from theelectrofilter 37 or removing any other types of organic materials fromthe bed, or raise the temperature of the bed to such a degree that astream of nitrogen will bring it in a substantially dry condition. Theedible oil, stream and drain-down liquid from the electrofilter 37 inthis cleaning step may be passed to a blowdown tank 96 through the drainline 94 for suitable disposal.

In addition, the described arrangement for cleaning the electrofilter 37is important in the case of an inadvertent displacement into the droptank 22 of improperly hydrogenated material, soap, or fatty material ofsuch undesired characteristics that it would contaminate theelectrofilter bed 77. In this instance, the use of the system as aninitial cleanup can be employed to remove such deleterious or undesiredsoaps, acids and the like from the bed of the electrofilter 37.

Although the specific organic liquid has been described as an edibleoil, the present invention is not limited to such non-petroleum oil andis equally applicable to other types, such as fats, animal and vegetableoils, and related organic liquids.

From the foregoing, it will be apparent that there has been provided anelectrofiltration system of apparatus and process well adapted forremoving inorganic solids from organic liquid streams. In particular,the system can be operated for extended periods of time with arelatively simple cleaning procedure. No contamination of the organicliquid product can occur from the electrofilter system during operationor cleanup. In addition, the organic liquid product prepared quickly inone electrofiltration step is equal to commercial productsconventionally obtained by multistep filtration. It will be understoodthat certain features and alterations of the present system may beemployed without departing from the spirit of this invention. This iscontemplated by, and is within, the scope of the appended claims. It isintended that the present invention is to be taken as an illustration ofthe present system.

What is claimed is:
 1. An electrofilter for removing solids from anorganic liquid stream of high resistivity comprising:(a) a vessel havingan internal flow path extending between inlet and outlet means forpassing the organic liquid stream through said vessel; (b) said vesselcontaining in said internal flow path a bed of chemically inert, hardgranular particles of a rigid, substantially incompressible material,said particles being nonspheroidal with a relatively discontinuoussurface configuration and a dielectric constant not in excess of about7; (c) means for establishing a d.c. electrical field within said bed ofan intensity sufficient for removing solids from the organic liquidstream by electrically induced adhesion of the solids on said particlesand providing a purified organic liquid stream to said outlet means; and(d) means for selectively cleaning at least a portion of said particlesof adhering solids comprising means for interrupting said electricalfield, passing a cleaning liquid through said bed at a rate of flowinsufficient to cause turbulence in said bed, to remove adhering solidsfrom said particles without disruption of the particles, and removingthe cleaning liquid with the removed solids from said particles beingcleaned.
 2. The electrofilter of claim 1 wherein said particles have adielectric constant between about 2 and about
 5. 3. The electrofilter ofclaim 1 wherein said particles are of a mineral containing crystallinesilicon dioxide.
 4. The electrofilter of claim 1 wherein said particlesare selected from the group consisting of flint, garnet, granite andfused quartz.
 5. The electrofilter of claim 1 wherein said particleshave Tyler screen sizes in the range from about 2 mm to about 13 mm. 6.The electrofilter of claim 1 wherein said particles are of crushed flintrock having an average size of about 2.5 mm.
 7. The electrofilter ofclaim 1 including (e) monitoring means for providing an indicatingsignal for undertaking the selective cleaning of said particles ofadhering solids when the purified organic liquid stream approachesconditions of increased solids content by solid-fillup of said bed. 8.The electrofilter of claim 2 wherein said monitoring means opticallyscans the purified organic liquid in said outlet means and provides anindicating signal for undertaking the selective cleaning of saidmaterial of adhering solids when the purified organic liquid streamdegrades to a predetermined optical quality by increased solids contentfrom solids-fillup of said bed.
 9. The electrofilter of claim 1 whereinsaid d.c. electrical field has a potential gradient above about 20 kvper inch spacing in said bed.
 10. The electrofilter of claim 9 whereinsaid d.c. electrical field has a potential gradient of about 40 kv perinch spacing in said bed.
 11. The electrofilter of claim 1 wherein saidmeans (d) for selectively cleaning at least a portion of said particlesof adhering solids comprises means for conducting in sequence the stepsof (i) terminating the flow of said organic liquid stream, (ii) passinga dry, inert non-oxidizing gas downwardly through said bed with saidd.c. field established therein to displace the purified organic liquidstream through said outlet means without displacing the adhering solids,(iii) interrupting said electrical field and (iv) passing a cleaningliquid through said bed at a rate of flow insufficient to causeturbulence in said bed, to remove adhering solids from said particles,and means for removing the cleaning liquid with the removed solids fromsaid particles being cleaned.
 12. The electrofilter of claim 11 whereinsaid particles are of a mineral containing silicon dioxide.
 13. Theelectrofilter of claim 11 wherein said particles are selected from thegroup consisting of flint, garnet, granite and fused quartz.
 14. Theelectrofilter of claim 12 wherein said d.c. electrical field has apotential gradient above about 20 kv per inch spacing in said bed. 15.The electrofilter of claim 11 including (e) monitoring means providingan indicating signal for undertaking the selective cleaning of saidparticles of adhering solids when the purified organic liquid streamapproaches conditions of increased solids content by solids-fillup ofsaid bed.
 16. The electrofilter of claim 15 wherein said monitoringmeans optically scans the purified organic liquid stream in said outletmeans and provides an indicating signal for undertaking the selectivecleaning of said particles of adhering solids when the purified organicstream degrades to a predetermined optical quality by increased solidscontent from solids-fillup of said bed.
 17. The electrofilter of claim15 wherein controller means receives said indicating signal of saidmonitoring means and responsively activates said means for selectivelycleaning said particles of adhering solids.
 18. The electrofilter ofclaim 17 wherein said monitoring means optically scans the purifiedorganic liquid in said outlet means and provides an indicating signalfor undertaking the selective cleaning of said particles of adheringsolids when the purified organic stream degrades to a predeterminedoptical quality by increased solids content from solids-fillup of saidbed.
 19. The electrofilter of claim 1 wherein said means for selectivelycleaning said particles includes means for circulating said cleaningliquid in a closed loop, including reservoir means, through said bed.20. The electrofilter of claim 11 wherein said means (d) (iv) forpassing a cleaning liquid through said bed is adapted to pass thecleaning liquid upwardly through said bed.